1. Field of the Invention
The present invention relates to sensors and, more specifically, to optical gas detectors.
2. Description of the Related Art
Gas analyzers are used in environmental monitoring, industrial process control, geologic exploration, and medical, analytical, and military applications. For example, gases such as hydrogen sulfide and sulfur dioxide accompany natural gas and are often present in industrial environments. Since exposure to these gases is a health hazard, low concentrations, typically in the range of parts per million (ppm), need to be detected.
Different analytical techniques such as optical spectroscopy, mass spectrometry, gas chromatography, electrochemical analysis, etc., may be used for detection of substances present in relatively low concentrations. One particular technique, optical spectrophotometry, is based on the absorption of electromagnetic radiation by the sample in a selected spectral range and is generally recognized to have relatively high sensitivity and speed of analysis. A spectrophotometric system typically has (i) a light source; (ii) a monochromator, which filters the light from the light source so that only a limited wavelength range is allowed to irradiate the gas sample contained in a sample cell; and (iii) a photo-detector, which measures the amount of light transmitted through the sample. Representative prior-art spectrophotometric systems operating in either ultraviolet (UV) or infrared (IR) parts of the spectrum are described, for example, in U.S. Pat. Nos. 5,936,250 and 6,344,648, the teachings of both of which are incorporated herein by reference. However, one problem with prior-art spectrophotometric systems is that they are relatively difficult to adapt for portable, particularly hand-held, applications.